Electrolytic plating methods, for example copper-plating, nickel-plating, cobalt and cobalt alloy-plating, zincing, or tinning, are carried out by means of soluble or insoluble anodes. When soluble anodes, also known as active anode systems, are used in an electrolytic plating operation, the anode dissolves during plating. The anode comprises a salt of the metal ion being plated. Accordingly, a balance between the dissolution of the soluble anode during plating to yield additional metal ion in the plating bath and metal ion reduction at the cathode allows for careful control of a steady state concentration of metal ion in solution. Insoluble anodes, also referred to as inert anode systems, do not dissolve during the electrolysis because insoluble anodes are constituted of an inert material. Typically, insoluble anodes comprise a carrier material coated with an active layer material. Typical carrier materials, including titanium, niobium, stainless steel, and other inert metals such as valve metals, become passive, i.e., non-corroding, under electrolysis conditions. Typical active layer materials, which are electron-conductive materials, include platinum, iridium, ruthenium, other precious metals, mixed oxides thereof, or compounds of these elements. Herein, the active layer can either be directly applied on the surface of the carrier material or can be placed on a substrate, which is spaced with respect to the carrier material. Substrate materials include the same types of materials appropriate for use as carrier materials, for example stainless steel, titanium, and the like.
Generally, electrolytic plating can be carried out by means of direct-current, pulse current, or pulse reverse current.
Additives are typically added to electrolytic plating baths, which additives act, for example, as brighteners, to increase the deposit hardness and/or the dispersion. Herein, organic compounds are preferably used as additives.
During the electrolytic plating operation, gases, for example oxygen or chlorine, are generated at the insoluble anode. These gases can oxidize organic additives contained in the electrolytic plating bath, which can lead to partial or even complete decomposition of these additives. Decomposition of the organic additives is disadvantageous for at least a couple reasons. First, the additives have to be periodically replenished. Second, degradation products of the additives cause disturbances, such that it becomes necessary to frequently renew or purify or regenerate the electrolytic plating baths, which is neither economically nor ecologically reasonable.
EP 1 102 875 B1 discloses a method for inhibiting organic additive oxidation in an alkaline electrolytic plating bath by separating the anode from the cathode with an ion exchanger membrane. This design has the advantage that organic compounds are isolated from the anode, which effectively prevents oxidation of the additives. However, this design requires more instrumentation, since the electrolytic plating bath requires a closed box with an anolyte around the anode and a catolyte around the cathode. Additionally, a higher voltage is required, which questions the economic efficiency of the design. Importantly, the structural solution proposed by EP 1 102 875 B1 is not applicable to every anode-cathode geometry, such as for coating the interior of tubes.
DE 102 61 493 A1 discloses an anode for electrolytic plating, which comprises an anode base body and a screen. The anode base body comprises a carrier material and a substrate having an active layer. The screen of the anode base body is located at a fixed distance from the anode base body and reduces the mass transport towards the anode base body and away from it. In contrast to the design according to EP 1 102 875 B1, the use of such an anode requires less instrumentation and also has the advantage that the additives contained in the electrolytic plating bath do not oxidize to such a high extent.
However, the anode described in DE 102 61 493 A1 is expensive. The anode base body of the anode is formed by combining two parts, and the fabrication process is both effort-intensive and expensive. The anode base body comprises a carrier material and an active layer. Titanium is typically used as carrier material. The active layer, however, comprises expensive noble materials such as platinum, iridium, mixed oxides of platinum metals, and diamonds. The anode described in DE 102 61 493 A1 is comparatively expensive, whereby the economic efficiency of an electrolytic plating method using such an anode is doubtful.